1. Field
The following description relates to time synchronization of a data communication system that serves a data relay transmission function, and more particularly, to a device and method for allowing reliable external and internal high time-resolution time synchronization and time data sharing by use of a simple structure at a low cost in a data communication system with multiple processors and line interfaces.
2. Description of the Related Art
High-speed data communication technology enables the reduction of time expenditure for data transmission between physically remote locations. Physical space is not a significant limiting factor in data sharing any more. To perform the same task, collaboration task, or distributed task at physically distant locations simultaneously or on a schedule, two locations' times have to be synchronized in accordance with a degree of precision for the task. In other words, distant spaces in which to perform time-synchronized tasks have to all share the same precise time.
With the development of automation technology, many processes and tasks are performed by an automation device under the control of a controller, the automation device being implemented as a complex automation device that incorporates one or more unit automation devices. The complex automation device internally divides a single task into a number of jobs to process. A plurality of controllers is present in the complex automation device, and when all controllers have the same time information, it is possible to complete the single task as a whole by executing the divided jobs in the automation device. In this case, the controllers within the automation device may be synchronized to a local time that is independent of an external device.
When automation devices of different groups are not located within a given area, but located at different areas by their groups, and especially when the groups are quite distant from one another, they must have the same time to execute a synchronized task. That is, only when the devices' internal time is synchronized to a common time exterior to the devices, not to an internal local time, they can consistently work together in the physically remote areas. For particular devices in different spaces to execute a task synchronously, time synchronization between the spaces is a prerequisite, and seamless data transmission/reception and information sharing for task execution are required.
In this regard, a data communication device is required to transmit and relay general data information, as well as time information, and to enable the sharing of external and internal time information. The data communication device should be able to adjust its time to an external master time through time synchronization and correction, and provide the same time information to a remote device requesting time information, based on the adjusted internal time. Thus, when the data communication device capable of data relay-transmission serves several functions like general-data relay-transmission, time sharing, and time correction, the remote devices are able to share the time, and synchronously perform a task.
The time synchronization and data relay functions of the data communication device may be implemented differently, depending on the configuration and location of the device. In addition, the data communication device has different numbers and capabilities of processors in use depending on the number of connection lines connected to the external device and the data processing capacity. A high-capacity high-performance data communication device has a plurality of independent processors, which are distributed in blocks. Generally, processors use time for data processing, data control and management, and record and storing of important log history. A number of processors need to have the same time, and this time should be synchronized to an external time.
The data communication device can provide and correct time information with respect to the external device, and perform internal time-based jobs if the data communication device includes a means for obtaining the time of a reliable external device, and a means for allowing internal processors to share the time of the external device.
A real time processing needs to be accompanied for sharing and recognizing time information accurately. On general-purpose OS, such as Linux, it is difficult to execute processing in real time with high time resolution by only using software. A data communication device operating on a general-purpose OS needs to employ an additional device and method for time synchronization at high time precision.